class_docstr: Runs an op when a metric has plateaued.
code: def keep_alive(self):
      if self._only_once and self._ever_ran:
          return False
      return True
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import tensorflow.compat.v1
  from tensorboard.backend.event_processing import event_accumulator
  from tensorboard.backend.event_processing import event_multiplexer
label_desc: Use image node_id 2 for calling the PlateauOpHook obj's underlying member method code with example usage: obj.keep_alive() and returns: True, False